EP3433120B1 - Operating liquid container with stiffening element and method for manufacturing an operating liquid container - Google Patents

Description

The invention relates to an operating fluid container made of thermoplastic material for a motor vehicle.

Furthermore, the present invention relates to a method for producing an operating fluid container made of thermoplastic material for a motor vehicle.

Operating fluid containers made of thermoplastic plastic in the sense of the invention are, in particular, but not exclusively, fuel containers for motor vehicles, washer fluid containers, oil containers, secondary liquid containers or additive containers for motor vehicles. Containers of the type mentioned at the outset are often produced by extrusion blow molding, HDPE (High Density Polyethylene) being particularly suitable for the production of extrusion blow molded containers.

In motor vehicles with an internal combustion engine, when an operating liquid container, in particular the fuel container, is subjected to heat, the operating liquid, e.g. the fuel is also heated so that the vapor pressure of the operating fluid rises and the operating fluid container is subjected to a corresponding internal pressure, as a result of which the fuel container is subject to deformation.

To vent an operating fluid container in the form of a fuel container, the latter is fluidly connected to an activated carbon filter for filtering out fuel vapors. The activated carbon filter is flushed by means of intake air during operation of the internal combustion engine, so that fuel vapors bound in the activated carbon can be supplied to the internal combustion engine.

Due to the purging process with intake air, the absorption capacity of the activated carbon filter can be limited.

In hybrid motor vehicles there is also another problem due to the reduced operating time of the internal combustion engine. Due to the reduced operating time of the internal combustion engine, an activated carbon filter that is fluidly connected to the fuel tank is flushed correspondingly less, so that less fuel vapor bound in the activated carbon can also be flushed out. This in turn means that activated carbon filters in hybrid motor vehicles have to be dimensioned larger. Furthermore, by venting the fuel tank via the activated carbon filter, further fuel is converted into the vapor phase, so that it would be advantageous to make the fuel tank stiffer and / or more pressure-resistant.

It is known from the prior art to stiffen the fuel tank by wrapping and / or stiffening elements within the fuel tank. However, wrapped fuel tanks are complex to manufacture and therefore cost-intensive. In addition, an effectively wrapped geometry limits the design freedom and thus the usable volume.

For introducing a stiffening element into the operating fluid container, it is known from the prior art to use the so-called "twin sheet blowmolding" method for producing the operating fluid container, in which either two web-shaped preforms are extruded from an extrusion head with two extrusion nozzles, or a tubular one Preform is separated into two sheet-like rags. The web-shaped preforms are each formed in a blow mold half of a multi-part blow molding tool by means of differential pressure. Then using an intermediate frame of the blow molding tool, which is positioned between the two blow mold halves, a stiffening element is positioned between the molded container shells of the operating fluid container and is still located in the cavities of the blow mold halves, and is connected to at least one inside of a container shell. Finally, the intermediate frame between the blow mold halves is removed, and by joining the container shells, the stiffening element is connected to a further inside of a container shell, so that the stiffening element can counteract deformations caused by pressure.

Fuel tanks, especially for petrol, are usually made from multi-layer co-extruded plastics. At least one barrier layer for hydrocarbons is embedded in the wall of the fuel tank. Therefore, the operating fluid container produced by means of the "twin sheet blow molding" process has the advantage that the barrier layer is not damaged when the stiffening element is introduced, so that no leakage for hydrocarbons is formed. However, the "twin sheet blow molding" process is time consuming and costly compared to blow molding a tubular preform.

An operating fluid container made of thermoplastic material for a motor vehicle is from the DE 10 2008 009 829 A1 known.

The object on which the present invention is based is to provide an improved operating fluid container which has increased pressure stability and which is faster and less expensive to produce.

This object is achieved by an operating fluid container with the features specified in claim 1. Advantageous configurations are described in the dependent claims.

Furthermore, the present invention is based on the object of providing a method for producing an operating fluid container from thermoplastic, by means of which an operating fluid container with increased pressure stability can be produced quickly and inexpensively.

This object is achieved by a method with the features specified in claim 9. Advantageous embodiments of the method are described in the claims dependent on claim 9.

An operating fluid container made of thermoplastic material according to the invention has two openings, which are arranged in opposite container walls of the operating fluid container. Furthermore, the operating fluid container has at least one stiffening element projecting through both openings. Two stiffening element ends engage behind the container walls from the outside, so that the stiffening element counteracts a deformation caused by the internal pressure of the operating fluid container. The operating fluid container according to the invention is characterized in that a stabilizing element is arranged between at least one stiffening element end and a container wall, the stabilizing element in each case having a through opening through which the stiffening element projects. Furthermore, the stabilizing element has a first and a second thermoplastic and is welded to a container wall.

Of course, the operating fluid container according to the invention can have a number of stabilizing elements corresponding to the number of stiffening element ends, each of which has a through opening through which the / a stiffening element projects.

The operating fluid container according to the invention has a high pressure stability, because the stiffening element, which can be designed, for example, as a stiffening strut or stiffening tube, counteracts a deformation caused by internal pressure. The stabilizing elements arranged between the container walls and the stiffening element ends prevent the container walls from creeping when the operating fluid container according to the invention is pressurized. In principle, it is known that the thermoplastic HDPE, which usually forms at least the outer layer of an operating fluid container, becomes plastic again under a continuous pressure load and tends to creep. The effective contact surface of the stiffening element on the container wall is increased by means of the stabilizing element, so that creeping of the container wall is effectively counteracted. Creeping of the container walls is further counteracted by the fact that the stabilizing element is designed as a two-component component, that is to say as a component having two thermoplastic plastics. A first thermoplastic plastic of the stabilizing element has the effect that the stabilizing element can be welded to a container wall. Another thermoplastic of the stabilizing element has an increased rigidity (eg polyamide), so that creep is effectively counteracted. Furthermore, polyamide, for example, effectively counteracts diffusion of hydrocarbons, so that the operating fluid container according to the invention has a reduced permeability to hydrocarbons. Furthermore, the operating fluid container according to the invention can be produced by extruding and shaping a tubular preform, so that both the manufacturing costs and the manufacturing time of the operating fluid container according to the invention are reduced.

The operating fluid container is designed in particular as a fuel container. The openings in the container walls are preferably arranged opposite one another. The stiffening element ends can also be referred to as stiffening element connecting sections. The ends of the stiffening element engage behind the openings from the outside, so that the stiffening element is also referred to as a tie rod.

The stabilizing element can also be referred to as an insert, insert component, intermediate element, intermediate component or as an adapter. The stabilizing element is designed as a two-component component, that is to say as a component formed from two plastics, in particular two thermoplastic plastics.

Each stabilizing element is thus sandwiched between a stiffening element end and a container wall. Since each stabilizing element is welded to a container wall, the first thermoplastic plastic of the stabilizing elements is welded to the container walls. As a result, the weldability of the first thermoplastic is compatible with the thermoplastic of the operating fluid container.

The stiffening strut is preferably tubular.

The stiffening element ends preferably have a first and a second thermoplastic and are welded to a stabilizing element in each case.

The correspondingly designed operating fluid container has a further increased stability, because the stiffening element can also counteract, for example, tensile forces caused by overpressure and, for example, negative pressure-induced compressive forces between the container walls. Furthermore, the correspondingly designed operating fluid container also has increased torsional rigidity. Furthermore, the operating fluid container designed in this way can be produced by means of a few process steps, so that the production costs for the appropriately designed operating fluid container are reduced.

The first and second thermoplastics are preferably the same first and second thermoplastics that also comprise the stabilizing element. Of course, the thermoplastic materials of the stiffening element can also be other thermoplastic materials than the stabilizing element. Compatibility of the plastics only has to be guaranteed with regard to weldability.

Consequently, the first thermoplastic plastic of the stiffening element ends is welded to the stabilizing elements.

The entire stiffening element preferably has the first and the second thermoplastic.

More preferably, the stabilizing element has a circumferential collar which is angled in the direction of an outside of the container, so that the stabilizing element forms a trough on the outside of the container.

A corresponding design of the stabilizing element increases a contact area between the stabilizing element and the container wall, so that the stability of the operating fluid container is increased. A corresponding design of the operating fluid container also has the advantage that the stabilizing element can be flush with the container wall.

The trough is preferably funnel-shaped.

All stabilizing elements preferably have a correspondingly designed collar.

The stabilizing element preferably has a wall enclosing its through opening, which forms a receiving space which is open to the outside of the container and into which the stiffening element end is received.

The wall encloses the passage opening in a plan view of the stabilizing element.

The wall is preferably cylindrical. The cylindrical wall consequently also encloses the end of the stiffening element.

Each stabilizing element preferably has a corresponding cylindrical wall.

The operating fluid container preferably has at least one cover, which closes the receiving space of the stabilizing element and seals it towards the outside of the container. In the case of a suitably designed operating fluid container, the emission path for, for example, hydrocarbons from the operating fluid container is blocked.

The covers can be formed, for example, from PA (polyamide) and / or from POM (polyoxymethylene). The covers are preferably welded to the cylindrical walls of the stabilization devices. Since the stabilization devices are designed as two-component parts, the welding between the cover and the stabilization device is carried out by a PA / PA or POM / POM weld.

The operating fluid container is preferably designed such that the stiffening element is formed in two pieces with a first stiffening element part and a second stiffening element part. The first stiffening element part projects through a first opening of a first container wall and the second stiffening element part projects through a second opening in a second container wall. The stiffening element end of the first stiffening element part engages behind the first container wall and the stiffening element end of the second stiffening element part engages behind the second container wall from the outside. Both the first stiffening element part and the second stiffening element part each have a connecting device opposite their stiffening element ends, by means of which the two stiffening element parts are connected to one another.

A correspondingly designed operating fluid container is optimized with regard to its manufacturing time. This is because the stiffening element parts are introduced into the operating fluid container from two opposite sides and are connected to one another within the operating fluid container.

A first connecting device is arranged in the stiffening element end of the first stiffening element part and a second connecting device is arranged in the stiffening element end of the second stiffening element part.

The first connecting device can comprise at least one latching receptacle and the second connecting device can comprise at least one latching tongue.

The first connecting device can comprise at least one latching hook and the second connecting device can comprise at least one latching prong.

The operating fluid container is preferably designed such that the respective stiffening element parts have a cutting device at the ends opposite the stiffening element ends for severing the container wall.

A suitably designed operating fluid container can be produced in a further shortened cycle time, because the openings in the container walls of the operating fluid container do not have to be circled / formed in a separate step, but can be formed by inserting the stiffening element parts into the operating fluid container.

The operating fluid container is preferably designed in such a way that the operating fluid container is produced by blow molding a tubular preform.

• Bereitstellen von zumindest einem eine Durchgangsöffnung aufweisenden Stabilisierungselement;
• Einbringen eines schlauchförmigen Vorformlings aus thermoplastischem Kunststoff in ein Blasformwerkzeug mit einem Formnest, welches die Kontur des Betriebsflüssigkeitsbehälters definiert;
• Ausformen des Vorformlings innerhalb des Formnestes, wobei der Vorformling das Stabilisierungselement formnestseitig umschließt und mit dem Stabilisierungselement verschweißt wird;
• Herstellen von zwei Öffnungen in einander gegenüberliegenden Behälterwänden des Betriebsflüssigkeitsbehälters;
• Einführen eines ersten Versteifungselementteils durch eine erste Öffnung und eines zweiten Versteifungselementteils durch eine zweite Öffnung, so dass zumindest ein Versteifungselementende der Versteifungselementteile in direktem Kontakt mit dem zumindest einen Stabilisierungselement steht, wobei die Versteifungselementenden die Behälterwände jeweils hintergreifen; und
• Verbinden des ersten Versteifungselementteils mit dem zweiten Versteifungselementteil mittels an den Versteifungselementteilen bereitgestellten Verbindungseinrichtungen.

The object on which the present invention is based is also achieved by a method for producing an operating fluid container made of thermoplastic with at least one stiffening element arranged between opposing container walls, which counteracts a deformation caused by internal pressure of the operating fluid container, the method having the following method steps:

• Providing at least one stabilizing element having a through opening;
• Introducing a tubular preform made of thermoplastic material into a blow molding tool with a mold cavity which defines the contour of the operating fluid container;
• Shaping the preform within the mold cavity, the preform enclosing the stabilizing element on the mold nest side and being welded to the stabilizing element;
• Making two openings in opposing container walls of the operating fluid container;
• Inserting a first stiffening element part through a first opening and a second stiffening element part through a second opening, so that at least one stiffening element end of the stiffening element parts is in direct contact with the at least one stabilizing element, the stiffening element ends each engaging behind the container walls; and
• Connecting the first stiffening element part to the second stiffening element part by means of connecting devices provided on the stiffening element parts.

The method is preferably designed such that the openings in the container walls lying opposite one another can be introduced into the container walls by means of a cutting device of the stiffening element parts opposite the stiffening element ends, in that the first stiffening element part is pushed through a first container wall and the second stiffening element part is pushed through a second container wall.

The correspondingly designed method offers the advantage that fewer method steps are necessary for producing the operating fluid container, since the method steps of creating openings in the container walls of the operating fluid container together with introducing / pushing a first stiffening element part through a first container wall and a second stiffening element part through a second Container wall are realized.

Figur 1:

eine schematische Schnittansicht eines erfindungsgemäßen Betriebsflüssigkeitsbehälters; und

Figuren 2 bis 4:

verschiedene Varianten der Verbindung der Versteifungselementteile miteinander.

Further advantages, details and features of the invention result from the exemplary embodiments explained below. The following show in detail:

Figure 1:

is a schematic sectional view of an operating fluid container according to the invention; and

Figures 2 to 4:

different variants of the connection of the stiffening element parts to one another.

In the following description, the same reference numerals designate the same components or the same features, so that a description of one component with respect to one figure also applies to the other figures, so that a repetitive description is avoided. Furthermore, there are individual features that are associated with an embodiment have been described, can also be used separately in other embodiments.

Figure 1 shows a schematic sectional view of an operating fluid container 10 according to the invention. The operating fluid container 10 is usually made from a thermoplastic. In the exemplary embodiment shown, the operating fluid container 10 is designed as a fuel container 10, but the operating fluid container 10 can also be designed to hold a urea solution or washer fluid or oil or the like.

Out Figure 1 it can be seen that a first opening 13 is arranged in a first container wall 11 of the operating fluid container 10. In a second container wall 12 of the operating fluid container 10, a second opening 14 is provided, which is arranged opposite the first opening 13. The operating fluid container 10 further comprises a stiffening element 20 which projects through the two openings 13, 14 and is designed as a tie rod 20. The stiffening element 20 is formed in two pieces and comprises a first stiffening element part 21 and a second stiffening element part 22. The two stiffening element parts 21, 22 are connected to one another. With regard to the type of connection of the stiffening element parts 21, 22, reference is made to the explanations relating to FIGS Figures 2 to 4 referred to below.

The first stiffening element part 21 projects through the first opening 13, which is arranged in the first container wall 11, and the second stiffening element part 22 projects through the second opening 14, which is arranged in the second container wall 12. A stiffening element end 23 of the first stiffening element part 21 engages behind the container wall 11 from the outside, and a stiffening element end 23 ′ of the second stiffening element part 22 engages behind the second container wall 12 from the outside, so that the stiffening element 20 counteracts a deformation caused by the internal pressure of the operating fluid container 10.

Out Figure 1 it can also be seen that the operating fluid container 10 in the exemplary embodiment shown comprises two stabilizing elements 30. A stabilizing element 30 is arranged between the stiffening element end 23 of the first stiffening element part 21 and the first container wall 11. Another stabilizing element 30 is arranged between the stiffening element end 23 ′ of the second stiffening element part 22 and the second container wall 12.

The stabilizing elements 30 each have a first and a second thermoplastic, with at least a first thermoplastic being compatible in terms of weldability with a thermoplastic from which the container walls 11, 12 are made. So that's in Figure 1 Upper stabilizing element 30 shown with the first container wall 11 and that in Figure 1 Stabilizing element 30 shown below is welded to the second container wall 12. In Figure 1 is indicated in the drawing for the stabilizing elements 30 that this consists of a layer consisting of the first thermoplastic (e.g. HDPE), which is in direct contact with the container wall 11, 12, and a layer consisting of the second thermoplastic (e.g. polyamide) is in direct contact with the stiffening element end 23, 23 '.

The second thermoplastic plastic of the stabilizing elements can be formed, for example, from PA or POM, which have a greater hardness than, for example, HDPE. For this reason, the stabilizing elements 30 will not thin out when the stiffening element 20 is subjected to tensile stress. Furthermore, a thinning of the first container wall 11 and the second container wall 12 is counteracted by the fact that the forces exerted on the first container wall 11 and the second container wall 12 via the stiffening elements 20 over a larger area, namely the respective contact surfaces between the stabilizing devices 30 and the container walls 11, 12 are transmitted. Therefore, in the operating fluid container 10 according to the invention, both the first container wall 11 and the second container wall 12 are less prone to creep when pressurized by the stiffening element 20.

The stiffening element ends 23, 23 'of the first stiffening element part 21 and the second stiffening element part 22 also have a first and a second thermoplastic material, so that the stiffening element ends 23, 23' are also welded to the respective stabilization devices 30 accordingly. Therefore, by means of the stiffening element 20, tensile forces caused by a negative pressure in the operating fluid container 10 can also be transmitted to the first container wall 11 and the second container wall 12. Furthermore, torsional forces can be transmitted to the first container wall 11 and the second container wall 12 by means of the stiffening element 20.

Out Figure 1 it can also be seen that each stabilizing element 30 has a circumferential collar 32 which is angled in the direction of a container outer side 16, so that the stabilizing elements 30 on the container outer side 16 each form a trough 33. By means of a corresponding design of the stabilizing elements 30 it can be achieved that the stabilizing elements 30 are flush with the container walls 11, 12 of the operating fluid container 10 and thus do not protrude from the outer surface of the container walls 11, 12.

Each stabilizing element 30 comprises a through-opening 31, through which the stiffening element 20 projects, surrounding wall 34, which in the exemplary embodiment shown is designed as a cylindrical wall 34. The cylindrical wall 34 forms a receiving space 35 open to the outside of the container 16. In the receiving space 35 of the in Figure 1 Stabilizing element 30 shown above, the stiffening element end 23 of the first stiffening element part 21 is received. In the receiving space 35 of the in Figure 1 The stabilizing element 30 shown below accommodates the stiffening element end 23 ′ of the second stiffening element part 22.

The receiving spaces 35 of the stabilizing elements 30 are each closed by a cover 36 and sealed off from the outside of the container 16. The covers 36 are preferably welded to the end faces of the cylindrical changes 34 of the corresponding stabilizing elements 30. The diffusion of, for example, hydrocarbons from the inside of the container 15 to the outside of the container 16 is reduced by an appropriate design.

In the Figures 2 to 4 is indicated that the stiffening element parts 21, 22 can be locked together in different ways in their penetration area. Alternatively, these can also be made using a rotary / snap connection (Bayonet lock), screw connection or a bayonet connection.

Figure 2 shows a schematic view of a snap-in connection, comprising a snap-in receptacle 24 and a matching snap-in tongue 26. For example, on the outside of a cylindrical section of the first stiffening element part 21, a plurality of snap-in receptacles 24 arranged at a distance from one another can be provided in the form of snap-in channels, into which circumferentially fastened to the insert Engage latches 26. For this purpose, the latching tongues 26 can be provided with latching springs 27 which spring into correspondingly designed latching recesses 25 of the latching receptacles 24, as shown in Figure 2A is shown. Figure 2A shows a longitudinal section through the latching.

Figure 3 shows an alternative variant of a snap connection of the first stiffening element part 21 to the second stiffening element part 22. It is provided that the cylindrical section of the first stiffening element part 21 is latched to the cylindrical section of the second stiffening element part 22 in each case over the entire circumference, with the inside circumferentially in the cylindrical Section of the first stiffening element part 21 locking teeth 28 are provided and on the outer circumference of the cylindrical portion of the second stiffening element part 22 a circumferential locking hook 29 is provided. It is clear to the person skilled in the art that, instead of circumferential locking prongs 28, locking means can also be provided discretely on the circumference of the cylindrical sections of the first stiffening element part 21 and the second stiffening element part 22.

In Figure 4 Finally, a kind of bayonet lock is shown in a highly simplified manner, over which the cylindrical Sections of the first stiffening element part 21 and the second stiffening element part 22 can be positively locked together.

Reference symbol list:

10th

Operating fluid tank / fuel tank

11

first container wall (of the operating fluid container)

12th

second container wall (of the operating fluid container)

13

first opening (of the operating fluid container)

14

second opening (of the operating fluid container)

15

Inside of the container

16

Container outside

20th

Stiffening element

21

first stiffening element part

22

second stiffening element part

23, 23 '

Stiffening element end / connecting section of the stiffening element

24th

Connection device / snap-in holder

25th

Connection device / locking recess

26

Connection device / locking tongue

27

Connection device / detent spring

28

Connection device / locking teeth

29

Connection device / locking hook

30th

Stabilizing element

31

Through opening / through opening (of the stabilizing element)

32

Collar (of the stabilizing element)

33

Trough (of the stabilizing element)

34

cylindrical wall (of the stabilizing element)

35

Receiving space (of the stabilizing element)

36

cover

Claims (11)

1. An operating fluid container (10) made of thermoplastic for a motor vehicle, comprising the following features:

   - the operating fluid container (10) has two openings (13, 14) in mutually opposite container walls (11, 12) of the operating fluid container (10), and a stiffening element (20) projecting through the two openings (13, 14); and

   - two stiffening elements (23, 23') engage behind the container walls (11, 12) from the outside, and therefore the stiffening element (20) counteracts deformation caused by the internal pressure of the operating fluid container (10),

   wherein the operating fluid container (10) is characterized by the following features:

   - a stabilizing element (30) is arranged between at least one stiffening element end (23, 23') and a container wall (11, 12);

   - the stabilizing element (30) has a passage opening (31) through which the stiffening element (20) projects;

   - the stabilizing element (30) comprises a first and a second thermoplastic; and

   - the stabilizing element (30) is welded to a container wall (11, 12).
2. The operating fluid container (10) as claimed in claim 1, characterized in that the stiffening element ends (23, 23') comprise a first and a second thermoplastic and are welded to one stabilizing element (30) each.
3. The operating fluid container (10) as claimed in either of the preceding claims, characterized in that the stabilizing element (30) has an encircling collar (32) which is angled in the direction of a container outer side (16), and therefore the stabilizing element (30) forms a trough (33) on the container outer side.
4. The operating fluid container (10) as claimed in one of the preceding claims, characterized in that the stabilizing element (30) has a wall (34) which surrounds the passage opening (31) therein and forms a receiving space (35) which is open to the container outer side (16) and into which the stiffening element end (23, 23') is received.
5. The operating fluid container (10) as claimed in claim 4, characterized in that the operating fluid container (10) has at least one covering (36) which closes the receiving space (35) of the stabilizing element (30) and seals same toward the container outer side (16).
6. The operating fluid container (10) as claimed in one of the preceding claims, characterized in that

   - the stiffening element (20) is formed in two pieces with a first stiffening element part (21) and a second stiffening element part (22);

   - the first stiffening element part (21) projects through a first opening (13) in a first container wall (11) and the second stiffening element part (22) projects through a second opening (14) in a second container wall (12);

   - the stiffening element end (23) of the first stiffening element part (21) engages behind the first container wall (11) and the stiffening element end (23') of the second stiffening element part (22) engages behind the second container wall (12), in each case from the outside; and

   - the first stiffening element part (21) and the second stiffening element part (22) each has, opposite their stiffening element ends (23, 23'), a connecting device (24 - 29), which connecting devices are used to connect the two stiffening element parts (21, 22) to each other.
7. The operating fluid container (10) as claimed in claim 6, characterized in that, at the ends opposite the stiffening element ends (23, 23'), the respective stiffening element parts (21, 22) have a cutting device for severing the container wall (11, 12).
8. The operating fluid container (10) as claimed in one of the preceding claims, characterized in that the operating fluid container (10) is produced by blow molding a tubular preform.
9. A method for producing an operating fluid container (10) made of thermoplastic with at least one stiffening element (20) which is arranged between mutually opposite container walls (11, 12) and counteracts deformation caused by the internal pressure of the operating fluid container (10), having the following method steps:

   - providing at least one stabilizing element (30) having a passage opening (31);

   - introducing a tubular preform made of thermoplastic into a blow mold having a mold cavity which defines the contour of the operating fluid container (10);

   - molding the preform inside the mold cavity, wherein the preform surrounds the stabilizing element (30) on the mold cavity side and is welded to the stabilizing element (30) ;

   - producing two openings (13, 14) in mutually opposite container walls (11, 12) of the operating fluid container (10) ;

   - inserting a first stiffening element part (21) through a first opening (13) and a second stiffening element part (22) through a second opening (14) such that at least one stiffening element end (23, 23') of the stiffening element parts (21, 22) is/are in direct contact with the at least one stabilizing element (30) wherein the stiffening element ends (23, 23') each engage behind the container walls (11, 12); and

   - connecting the first stiffening element part (21) to the second stiffening element part (22) by means of connecting devices (24 - 29) provided on the stiffening element parts (21, 42).
10. The method as claimed in claim 9, characterized in that the openings (13, 14) in the mutually opposite container walls (11, 12) are introduced into the container walls (11, 12) by means of a respective cutting device of the stiffening element parts (21, 22) opposite the stiffening element ends (23, 23') by the first stiffening element part (21) being pushed through a first container wall (11) and the second stiffening element part (22) being pushed through a second container wall (12).
11. The method as claimed in either of claims 9 and 10, characterized in that the stiffening element ends (23, 23') comprise a first and second thermoplastic and are welded to one stabilizing element (30) each.

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